Recently, problems such as signal delay due to electric wiring, generation of heat, generation of EMI (electromagnetic radiation noise), and so on have been surfaced in the connection between electronic devices such as boards, computers, peripheral devices, and so on. For solving such problems arising in electric wiring, optical interconnection, that is constructed by use of a silicon photonics technique, is being developed (Non-patent-related Document 1). The silicon photonics is a technique relating to optical elements, and it uses silicon as material; and the optical interconnection is a technique for communicating signals by converting electric signals from an external device into optical signals and converting optical signals into electric signals. In Non-patent-related Document 1, an example of signal transmission between LSI chips is shown; however, transmission of converted signals between devices, in which the transmission is carried out by use of fibers via optical connectors, is also possible.
Regarding such optical interconnection in an opto-electric hybrid board, it is required to construct the opto-electric hybrid board in such a manner that the construction of connection for inputting/outputting electric signals and the construction of connection for inputting/outputting optical signals do not interfere with each other; and it is also required that the opto-electric hybrid board has a structure that makes possible to carry out electrical connection in a simple manner, and has a construction that makes possible to carry out precise and simple optical connection in a simple manner by simplifying the construction of optical connection.
FIGS. 1 and 2 are schematic top views that show prior-art optical integrated circuits for optical transmitters placed on opto-electric hybrid boards. In FIG. 1, arrangement of typical optical elements such as optical waveguide elements and so on is shown. On the other hand, in FIG. 2, optical waveguide elements and so on are not shown; however, instead thereof, arrangement of circuit elements such as input pads (electrically conductive pins in this example) for high-speed electric signals, a driver IC, and so on is shown. This type of optical integrated circuit can be downsized and made to be highly dense by forming it within a silicon substrate by using the silicon photonics technique.
In an optical integrated circuit 100 in FIG. 1, the laser light, that is emitted by a semiconductor laser 1 and inputted via optical coupling, propagates through an optical waveguide 3 via a spot size converter 2; and the laser light is coupled to a coupler (an MMI coupler) 4. In the optical coupler 4, the laser light is divided into plural pieces of input light, and the pieces of the input light propagate through optical waveguides 5a that are constructed as curved waveguides having curved parts 5a; and the pieces of the input light are inputted to an optical modulator array 60 in which plural optical modulators are arranged. The optical signals outputted from the optical modulator array 60 are coupled, via optical waveguides 7, to an optical signal outputting element array 80 in which plural optical signal outputting elements are arranged; and the optical signals are outputted from the optical signal outputting elements to the outside via optical fibers and so on.
As shown in FIG. 2, in an opto-electric hybrid board, an electric I/O array 90 that is formed by arranging, along fringe parts of the board, plural input pads for electrical connection for high-speed electric signals, and a driver IC 50 for controlling optical modulation are placed; and electrical connecting wires 95 of high-speed electric wiring are further formed on the opto-electric hybrid board. On the opto-electric hybrid board, the area for placing the driver IC 50 overlaps with the area of the optical modulator array 60; the driver IC is placed above the optical modulator; and the direction of propagation of the light within the optical modulator and the direction of propagation of the electric signal within the driver IC coincide with each other. Thus, the laser 1 is placed in such a manner that it avoids the electric I/O array 90 and the electrical connecting wires (in this example, it is placed on a corner part of the plane).
Although the above is shown as an example of an optical integrated circuit for an optical transmitter, an example of a transmission unit in an optical transmitted/received is similar to that described above.